A blister package is made by heat molding a plastic sheet to form a plastic container having one or a plurality of recessed spaces, putting an article to be stored therein, covering the opening of the container with a substrate such as a plastic film, an aluminum foil, and so on, and adhering the periphery of the article.
Such a blister package may increase the display effect of an article, and indicate a method of use and so on on a substrate part thereof, and thus is applied for packaging of various articles such as foods, batteries, toothbrushes, medicines, stationery, and so on.
In the blister package, the plastic container and the substrate are adhered mainly by heat sealing. For this, a resin having heat sealability is applied for the formation of the plastic container, and a resin having heat sealability is also coated on the substrate.
For example, for the blister package, a forming film, a lidding material, a heat seal coating, and so on, are required. Among them, since the forming film and the lidding material are combined to form one integrated blister package, the adhesion property of the heat seal coating is very important.
Thus, for the resin applied for the heat seal coating of a blister package, stable heat sealability (that is, the property of exhibiting adhesion at high temperature and/or high pressure conditions without exhibiting adhesion at room temperature) is basically required, and coating suitability for the plastic container and the substrate is required.
Previously, an oil-based resin solution was used as a coating solution exhibiting heat sealability. However, due to combustibility of the oil-based resin solution, there is a risk of fire, and an organic solvent may remain in the package.
Particularly, since the blister package is mainly applied for foods, medicines, stationery, and so on, an organic solvent remaining in the package would directly affect on a human body, and thus the oil-based resin solution is not suitable.
In order to compensate the disadvantage, a method of applying a water soluble styrene/acryl-based resin to the heat seal coating of a blister package has been suggested.
However, heat seal coating resins for a blister package suggested until now not only have lowered heat sealability compared to previous oil-based resins under the same temperature conditions (for example, 150 to 160° C.), but also have problems of deformation of the plastic container of the blister package when heated to a temperature at which heat sealing is enabled.